1. Field of the Invention
The present invention relates to a thermal printer and a related method, and more particularly, to a thermal printer and a related method for printing a plurality of color blocks to media for printing images.
2. Description of the Prior Art
Thermal transferring printing technology was first researched in the early 80s by Fujicopian Co., Ltd. Afterward, this proprietary technology was transferred to American research organizations to develop via International Imaging Materials, Inc. The first commercial thermal printer appeared in 1986. Thereafter, thermal transferring printing systems have undergone many improvements and revolutions. As the demand for polychrome imaging increases and the ratio of possession of digital cameras keeps increasing, not only businesses but the general public also need a way to print their polychrome photos. However, because of a thermal diffusion effect brought by heating a point, the resolution of most thermal transferring was not very good in the early stages.
The material of the transferring ribbon adapted by common thermal printers is a kind of transparent celluloid paper containing wax and dye. The thermal print head heats the dye of the transferring ribbon when printing. When the temperature increases, the dye liquefies temporarily and moves from the transferring ribbon to a medium (paper for example). Then the dye cools and solidifies on the medium to display an image. Please refer to FIG. 1. FIG. 1 is a diagram of a polychrome transferring ribbon of a conventional thermal transferring process. As illustrated in FIG. 1, there are consecutive color blocks 141 and 142 on a polychrome ribbon 12. There are dye blocks of different colors and an overcoating block in each color block. For example, there is a yellow dye block 1Y1, a magenta dye block 1M1, a cyan dye block 1C1, and an overcoating block 1O1 in color block 141. When a thermal printer of the prior art prints a polychrome image, the thermal printer head heats dye blocks of different colors and an overcoating block in a color block on a polychrome ribbon in turn, and transfers the dye and the overcoating to a medium. Taking the polychrome ribbon 12 and the color block 141 for example, the thermal print head heats and transfers the dyes of yellow dye block 1Y1, magenta dye block 1M1, and cyan dye block 1C1 in turn from a starting point 161, and then heats overcoating block 1O1 to cover the output image with the overcoating. The process of thermal transferring ends up at an end point 181. FIG. 2 is a cross-sectional diagram of a result of a conventional polychrome thermal transferring technology. M1 is a medium to display an output image. LY1, LM1, and LC1 are a yellow dye layer, a magenta dye layer, and a cyan dye layer, respectively. LO1 is an overcoating layer.
Please refer to FIG. 3. FIG. 3 is a diagram of a monochromatic transferring ribbon of a conventional thermal transferring process. As illustrated in FIG. 3, there are consecutive color blocks 341 and 342 on a monochromatic ribbon 32. Each color block contains a black dye block and an overcoating block. The color block 341 contains a black dye block 3K1 and an overcoating block 3O1. When a thermal printer of the prior art prints a monochromatic image, the thermal printer head heats a black dye block and an overcoating block in one color block in turn, and transfers the dye and the overcoating to a medium. Taking monochromatic ribbon 32 and color block 341 for example, the thermal print head heats and transfers the dye of black dye block 3K1 from a starting point 361, and then heats overcoating block 3O1 to cover the output image with the overcoating. The process of thermal transferring ends up at an end point 381. FIG. 4 is a cross-sectional diagram of a result of a conventional monochromatic thermal transferring technology. M3 is a medium to display an output image, LK3 is a black dye layer, and LO3 is an overcoating layer.
Since the thermal print head can control the heating time to determine the amount of dye to transfer, the color output of a thermal printer is more accurate than that of an ink jet printer or other type of printer, and the number of colors available are as many as to approach true color. The performance is more similar to photo quality than output of the ink jet printer. For instance, a printer capable of continuous color hues can display a smooth grayscale from white to black, but a printer only capable of discrete color hues, like an ink jet printer, can only emulate the true colors of an image by dithering, which cannot compete with the quality of continuous color hues. Regarding preservation, the protective overcoating layer output by the thermal printer provides advantages in waterproofing, UV-ray proofing, and fingerprint proofing over other technologies. Therefore, the overall performance of thermal printers is much better than that of other printers, even though the resolution of thermal transferring printers is not relatively high.
The principle of thermal transferring of the prior art is to heat dye on a transferring ribbon by a thermal print head, temporarily liquefy the dye and transfer it to a medium, and then solidify the dye to display an image. However, the material of the transferring ribbon (transparent celluloid paper usually) readily becomes deformed and rippled if it has been heated for too long. Therefore, if the grayscale or the saturation of colors of the output image is high, the thermal print head heats the transferring ribbon for a longer time and a ripple effect is generated on the medium. To avoid this kind of distortion, the thermal printer of the prior art limits the successive heating time so the thermal print head does not provide too much heat, and thus, is not able to print images with higher saturation and wider dynamic range of color.
In order to overcome this problem of insufficient saturation and dynamic range of color, improving the quality of transferring ribbons has been the focus of the prior art. However, further improvement is restricted since the ceiling of the technology has nearly been reached.